The present invention relates to substrate processing, and more particularly to a method and apparatus for improved substrate handling.
Cluster tools are commonly used in the fabrication of integrated circuits. A cluster tool typically includes a load lock chamber for introducing substrates (e.g., semiconductor wafers) into the tool and a central transfer chamber for moving substrates between the load lock chamber and a plurality of processing chambers and one or more cool down chambers mounted on the transfer chamber. Typically, either a single blade or a double blade robot is located within the transfer chamber to move substrates between the load lock chamber, the processing chambers, the cool down chamber(s) and then back to the load lock chamber. Exemplary cluster tools, robots and substrate handling methods are described in U.S. Pat. Nos. 4,951,601 and 5,292,393, both of which are incorporated herein by reference in their entirety.
Within a cluster tool a typical substrate handler arm capable of 360xc2x0 rotation and extension is positioned inside the central transfer chamber. In operation the substrate handler rotates to align its blade with a sealable slit (e.g., a slit valve) which connects the central transfer chamber to a load lock chamber (i.e., a load lock slit). The substrate handler extends through the load lock slit, picks up a substrate, retracts, rotates to position the substrate in front of a processing chamber slit (which connects the central transfer chamber with the processing chamber) and extends through the slit to place the substrate in the processing chamber. After the processing chamber finishes processing the substrate, the wafer handler extends through the processing chamber slit, picks up the substrate, retracts and rotates to position the substrate in front of a cool down chamber slit. The substrate handler again extends placing the substrate in the cool down chamber and then retracts therefrom. After substrate cooling is complete, the substrate handler extends through the cool down chamber slit, picks up the substrate and retracts through the cool down chamber slit in order to extract the substrate and carry the substrate to another processing chamber or return the substrate to the load lock chamber. While the substrate is processing or cooling, the substrate handler places and extracts other substrates from the remaining chambers (e.g., load lock, processing or cool down chambers) in the same manner. Thus, the substrate handler undergoes a complex pattern of rotations and extensions, requiring a mechanically complex and expensive substrate handler. Further, each substrate handler extension and rotation requires considerable operating space and may introduce reliability problems.
One way to improve system efficiency is to provide a robot arm having the ability to handle two substrates at the same time. Thus, some equipment manufacturers have provided a robot arm in which two carrier blades are rotated about a pivot point at the robot wrist (e.g., via a motor and belt drive positioned at the substrate handler""s wrist). Thus, a first substrate (e.g., to be processed) may be stored on one blade while the other blade picks up a second substrate (e.g., previously processed). The carrier blades are then rotated and the first stored substrate is placed as desired. Such a mechanism is rather complex and requires a massive arm assembly to support the weight of a carrier blade drive located at the end of an extendible robot arm. For example, three drives are usually required for a system incorporating such a robot arm: one drive to rotate the arm, one drive to extend the arm, and one drive to rotate the carrier blades. Any improvement in throughput provided by such a multiple carrier robot comes at a price of increased equipment/manufacturing cost, increased weight and power consumption, and increased complexity and, thus, reduced reliability and serviceability.
Another approach places two robot arms coaxially about a common pivot point. Each such robot arm operates independently of the other and improved throughput can be obtained through the increased handling capacity of the system. However, it is not simple to provide two robot arms for independent operation about a common axis. Thus, multiple drives must be provided, again increasing manufacture/equipment costs and complexity while reducing reliability.
The various processes which are performed on the various substrates, may require different processing times. Therefore, some substrates may remain in a chamber for a short period of time after processing is completed before they are moved into a subsequent processing chamber because the subsequent processing chamber is still processing another substrate. This causes a substrate back log and decreases system throughput.
In addition to varying processing times, another factor which affects throughput is the need to cool individual substrates following processing. Specifically, the number of movements a substrate handler must make in order to process numerous substrates increases significantly when the substrates must be transferred to one or more cool down chambers following each processing step. Additionally, incorporation of one or more cool down chambers reduces the number of positions on the transfer chamber where a processing chamber may be positioned. Fewer processing chambers can result in lower system throughput and can increase the cost of each wafer processed.
Therefore, there remains a need for a method and apparatus for improved substrate handling module which can increase substrate throughput while preferably providing substrate cooling.
Embodiments of the present invention improve upon the xe2x80x9cCarousel Wafer Transfer Systemxe2x80x9d described in U.S. patent application Ser. No. 09/332,207 from which this application is a continuation-in-part. Various embodiments of the invention provide aspects which enhance substrate heating and cooling efficiency, reduce substrate handler complexity, reduce contact between moving parts during substrate transfer operation (e.g., reducing particle generation associated therewith), improve substrate handling equipment reliability, and/or increase substrate throughput.
In a first aspect, the invention comprises a temperature adjustment plate located below a substrate carriage (such as the rotatable carousel described in the parent application Ser. No. 09/332,207) and configured such that a substrate may be transferred between the temperature adjustment plate and the substrate carriage, by lifting and lowering the substrate carriage above and below the top surface of the temperature adjustment plate. The temperature adjustment plate may be configured to heat and/or cool a substrate positioned thereon.
In a second aspect, the substrate carriage is magnetically coupled so as to rotate and/or lift and lower magnetically, thereby reducing particle generation via contact between moving parts (and potential chamber contamination therefrom).
In a third aspect, a substrate handler positioned below the substrate carriage is both magnetically coupled and magnetically levitated, providing further particle reduction. The magnetic levitation is preferably achieved via four radially disposed and vertically arranged magnet pairs having distance sensors for maintaining desired spacing therebetween.
In a preferred embodiment, one substrate is heated/degassed on a first portion of a temperature adjustment plate in preparation for processing while a second substrate is processed, and a third processed substrate is cooled on a second portion of the temperature adjustment plate. An advantage of this arrangement is that the chamber containing the substrate carriage requires only a small volume of operating space, and may be quickly pumped to vacuum pressure. Thus, certain embodiments need not employ a separate load lock chamber.
Other features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.